Scanning mirror redesign of the EasyScan retinal imaging system
V. Čechanavičius (TU Delft - Mechanical Engineering)
J.P. Kappelhof – Mentor (TU Delft - Optical Technologies)
S.H. Hassan HosseinNia – Graduation committee member (TU Delft - Mechatronic Systems Design)
N Bhattacharya – Graduation committee member (TU Delft - ImPhys/Medical Imaging)
Erik van Dijk – Graduation committee member (EasyScan B.V.)
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Abstract
EasyScan is a scanning system, which images the retina. The condition of the retina can help identify various diseases, such as glaucoma, diabetic retinopathy, cataract, macular degeneration and others. It is a commercially successful device that has sold thousands of units worldwide. However, the scanner is facing lifetime issues, as the scanner mirrors will become obsolete in the foreseeable future. Possible ways of improving the optical system by reducing the required scan amplitude were investigated. Optical tests with fine pitch lenticular lenses, diffractive optical elements, and linear diffuser were conducted. No optical improvement was achieved; therefore, the scanner design was based on the functional requirements of the original system. Actuation methods and guiding mechanisms for low cost, low volume applications were studied. The proposed design for both the low frequency (LF) and high frequency (HF) scanners is a compact reluctance force actuated scanner mirror. However, design issues for the LF scanner guiding mechanism were encountered, that could not be solved in time. Nonetheless, a prototype of the HF scanner was finalized and managed to achieve the required $\pm$\SI{3}{\milli\radian} amplitude at a frequency of \SI{4650}{\hertz}. The scanner was validated on an actual EasyScan optical module. However, reliability issues still need to be solved before making the scanner production ready, for which possible solutions are discussed.